Pete,
the way Pat normally does his dihedral is as stated, build the wing in halves,, block up the tips. Join the leading edge, sheeting, and spars. Then after that is set, sheet the center section to lock it all in. Pat normally also installs only half the shear webs until after the wing is virtually done. That way he can adjust the wings straightness by using the remaining shear webs to lock it all in place.